Biotic resistance, facilitation and management of novel ecosystems

Humans have altered natural ecosystems such that the biotic and abiotic attributes have greatly changed from the historic ecosystem. One of the ways that these `novel ecosystems' are altered is through the addition of non-native species to communities and ecosystems, thereby altering not only the composition of species but also the species interactions. Novel Ecosystems pose several challenges for managers. First, managers need to understand what community and ecosystem attributes make the system more invasible. Two theories in invasion biology predict why some communities are more invasible than others. First, communities with greater abiotic heterogeneity would support more species; including invasive species, making them more invasible. Second, increased native diversity should decrease the available niche space for new invaders making a community less invasible. In addition, recent research has also demonstrated that native predators provide biotic resistance to invasion, however theory would predict that predators should also facilitate invasions in some circumstances. To test the heterogeneity and diversity hypotheses, we submerged small panels with varying combinations of vertical and horizontal surfaces and varying degrees of species richness off of a floating dock. We found that species diversity and abiotic heterogeneity along with species identity need to be considered together to determine how invasible a community is. To test the hypothesis that apex predators decrease invasions, we submerged caged and uncaged panels on pier pilings. Half of the panels had mussels and the others were left bare. We excluded sea stars from half of the pilings by wrapping bird spikes around the piling bases. We found that both sea stars and otters increased abundance of the non-native bryozoan, Watersipora subtorquata. Inavasive species are one of many threats to marine ecosystems. However, management of novel marine ecosystems must take into consideration all of the potential threats and desired services. In some situations, management actions for desired services may conflict with one another creating tradeoffs while in other situations a management action may have a positive effect on multiple services. To identify optimal management actions and those management actions with tradeoffs, we identified potential services and management actions. We then created a matrix that estimated the effect of one management action across all services. The matrix can be used as a tool for optimizing management of estuarine ecosystems.